Chris Weidman might have said it best, moments after knocking out Anderson Silva for the UFC middleweight title in July: No one is invincible.

If 2013 reminded us of one thing, it’s that no one is untouchable in mixed martial arts. Not every UFC belt changed hands, but dominant champs such as Georges St-Pierre, Jon Jones and Ronda Rousey each danced with defeat at some point this year.

Silva had lost before Weidman knocked him unconscious, but not since 2006 and never in the UFC. We all tend to agree with the general idea that no fighter is “perfect,” but Silva has been, in the eyes of many, the closest thing to it.

His loss, to an undefeated fighter no less, highlights an interesting question: What is perfect relative to MMA? Will we ever see a fighter pitch a career shutout -- an undefeated record at the highest level? Is it even possible?

In the minds of those who still have a shot at retiring undefeated, it’s quite possible.

“Absolutely,” said light heavyweight champion Jon Jones, when asked whether the UFC will ever see one of its champions retire undefeated. “If I were to retire right now, I would consider myself undefeated, so it’s totally doable.

“I’ve felt [unbeatable] a lot of times throughout my career, watching my old fights and seeing the way I’ve dominated people. I’ve definitely felt invincible at times. I think it’s important to feel that way, but still respect your opponent.”

Despite one loss (via disqualification), Jon Jones feels as though he can walk away from the sport as an "undefeated" fighter. Ed Mulholland for ESPN

There are currently (and this number might surprise you) 32 fighters on the UFC roster who have yet to lose as a professional. Of those 32, however, 23 have fought 10 times or fewer and are well outside of title contention. Jones is 19-1, the "1" thanks to a disqualification in 2009.

The competition level of the UFC will spoil undefeated records pretty quickly, says Weidman (10-0), who still believes that it's possible for a fighter to retire undefeated but that his or her final record would look nothing like that of boxer Floyd Mayweather Jr., who is 45-0.

“There are more ways to lose in MMA,” Weidman said. “You have striking, wrestling; there’s always a guy that’s going to come around that might have something better than you.

“You could have a guy go [undefeated], but not with the numbers of a Mayweather. I don’t know about that many fights. And in boxing, they start you off fighting 15 guys with losing records. In MMA, you get thrown in right away. I’m 10-0, and I’m already the champion.”

The greatest challenge of remaining perfect, it seems, is finding a perfect balance in multiple aspects of the sport.

You have to feel invincible, but know you’re vulnerable. You have to fear losing, but remain unaffected by the pressure of that fear. You have to win every training session, but hold back enough to not injure yourself in the process.

“When I’m about to fight, I am laser focused on my fear of failure,” said Rousey, a former U.S. Olympian in judo and 7-0 in MMA. “That’s why I try to raise the stakes in every fight, because I’m more likely to make a mistake when I feel it’s not a big deal.

“The mental thing is really the hardest part. I think if they would line up 20 fights and I could have them happen in a week, it would be easier for me to do it than over the course of several years. It’s the buildup to every fight that takes it out of you.”

Of course, there is also the challenge of walking away from competition itself with a perfect record intact. This year, St-Pierre essentially became the first modern-era UFC champion to willingly vacate his belt -- and even he left the door open for a return.

Frank Shamrock vacated the UFC middleweight title (now the light heavyweight title) when he retired in 1999. He had seven losses on his record before that decision. He returned after a brief absence and suffered three more defeats.

Bas Rutten vacated the UFC heavyweight belt that same year and announced his retirement, although he would return for one pro fight seven years later. He finished his career with a record of 28-4-1.

Phillip Miller retired from professional MMA in 2003 with a perfect 16-0 record, including two appearances in the UFC, but he never fought for a title. Royce Gracie was 11-0-1 when he left the UFC in 1995, but he returned to action five years later and eventually lost to Matt Hughes at UFC 60 in 2006.

Depending on what way you look at it, several have come close to sort of walking away from the highest level of MMA undefeated -- but it’s a distinction no one can legitimately, inarguably claim thus far.

Frankly, odds seem very much against it. There are too many ways to lose in MMA.

Jones was disqualified for a rarely used rule in a fight he was dominating. Heavyweight Travis Browne suffered his first loss when he tore his hamstring muscle in a freak-accident type injury against Antonio Silva. Seemingly unstoppable Cain Velasquez lost his perfect record in a split second, thanks to a Junior dos Santos right hand.

In the words of Silva, speaking to ESPN.com, “A perfect fight doesn’t exist. You can only dream about a perfect fight.”

If a perfect fight doesn’t exist, how reasonable is it to believe that a perfect record could? Well, there are those who do.

“My mom says there’s never a history of anything happening until it does,” Rousey said. “And then there it is.”